Up until a couple of days ago I was able to emulate the middle button when activating both the left and right button at the same time.

For some reason I'm no longer able to do this. I suspect that this stopped working after a recent update to something that deals with xorg. I see from looking at the apt history log file that xserver-xorg-core & xserver-common were recently updated.

Is it possible that one of these update could have broken my middle button emulation?